they immediately blew up and demanded "look at me when we're talking!"
I have no idea if it's a thing at all but frankly that sounds a bit rude regardless, doubly so since they were presumably aware you had different cultural cues
Barely related, your story reminds me of one time younger I gave a presentation to visiting teachers from Bangalore. I had rarely interacted with Indian people at the time; and they do this thing in South India where they shake their head in some sort of vague way (it's hard to describe) to basically say "yes" or "continue". Except I had never encountered the gesture, and I spent the entire presentation increasingly getting more panicked wondering why the fuck these seniors dude kept shaking their heads like "no" / "I don't agree", slide after slide, genuinely wondering if I was talking nonsense. And even more confused why they seemed OK and agreeable despite it afterwards.
For what it's worth, I get it. When my partner started to feel a headache she tested immediately and opted to sleep on the sofa herself with a N95. And I did not catch it thanks to this. And when I got it months later I immediately did the same. I would be pissed too.
It's easy enough to understand your partner's attitude given basically close to absolutely everyone doesn't seem to even pretend there is a still-mutating virus with many unknowns going around though, sadly. Which is infuriating.